We have continued studies of chromatin structure, of the structural differences between transcriptionally active and inactive chromatin, and the possible role of left-handed Z DNA in chromatin structure. We have shown that a DNA segment 115 base pairs long, near the 5' end of the chicken adult Beta globin gene, can be released in high yield from red blood cell nuclei by digestion with MspI endonuclease. The release occurs only in nuclei transcribing the globin region and shows that a special nucleosome-free region, probably related to gene expression, exists in such cells. We have also studied the effects of high mobility group proteins on folding of chromatin, and the effect of chemically blocking the large groove of DNA on nucleosome formation. We have also shown that the presence of left-handed Z DNA has a major effect on the ability of DNA to form nucleosomes.